Polyunsaturated fatty acids are mixed in compositions for external use (e.g., cosmetics and external-use pharmaceuticals) in anticipation of skin-whitening effect, etc. However, polyunsaturated fatty acids are known to have poor stability over time, and the polyunsaturated fatty acid content of the compositions decreases over time. Furthermore, compositions blended with polyunsaturated fatty acids may be colored or develop bad smells. Particularly in Japan, laws, regulations, etc., require compositions for external use containing a polyunsaturated fatty acid as an active ingredient to stably retain 90% or more of the polyunsaturated fatty acid based on the specified amount for three years after production. Therefore, the development of effective stabilization techniques has been desired. For example, the following techniques have been proposed to improve the stability over time of polyunsaturated fatty acids: a technique of mixing eugenol, isoeugenol, vitamin K, or the like (PTL 1); techniques of mixing esterified polyunsaturated fatty acids (PTL 2 to PTL 4); a technique of producing an aerosol comprising nitrogen gas and a content containing a highly unsaturated fatty acid-containing lipid (PTL 5); and a technique of producing an emulsion in which a polyunsaturated fatty acid is mixed with a specific amount of a dispersing agent, such as vitamin E (PTL 6).